Recoil starters are widely employed with small internal combustion engines such as those used to power lawn mowers, outboard motors, and the like. Such starting apparatus commonly employs a pulley rotatably mounted on a shaft in concentric relationship to the engine flywheel and a rope is wound about the pulley for rotating the same. Drive mechanism in the form of a cup concentrically mounted upon the engine flywheel includes abutments or teeth which are selectively engaged by one or more pawls mounted upon the pulley structure. Pawl operating means is mounted upon the pulley shaft for extending the pawl or pawls radially outward into driving engagement with the engine cup abutments during rotation of the pulley in a cranking direction by tensioning the pulley rope. The pawls will automatically retract when the pulley is rotated in a non-cranking direction by a recoil spring of the coil type producing a biasing force on the pulley in a direction opposite the cranking direction. Pawls also retract without influence of pulley rotation whenever the engine rotates faster then the pulley as at the finish of the tensioning cycle or when the engine starts. Recoil starters of this general type are disclosed and explained in the assignee's U.S. Pat. No. 3,081,760 and 3,782,355.
Recoil starters of the aforementioned type pivotally mount the pawls upon pulley hub structure and the operating member for the pawls is either in the form an annular cup or a relatively flat plate. The cup or plate is rotatably mounted on and frictionally biased to the pulley shaft through a torsional drag brake mechanism, usually a spring, such that the cup or plate will initially not rotate with the pulley, but upon full extension of the pawls the drag brake will be overcome and the same will rotate with the pulley. The drag brake is sufficient to radially extend the pawls for engagement with the engine flywheel mounted abutment teeth while light enough to allow rewinding of the pulley or over running of the flywheel teeth past the pawls.
For purposes of symmetry and distribution of forces it is highly desirable that the pawls be employed in pairs or sets, and when two pawls are utilized they are mounted in a diametrical relationship with respect to the pulley hub, for this reason, but it is not uncommon for only a single pawl to engage an abutment producing asymmetrical forces. Because of the typical type of mounting of the starter housing upon a light sheet metal engine cooling shroud, flexing and misalignment occur.
Also, as high impact forces occur between the pawls and the engine flywheel mounted teeth wear at the end of the pawls occurs and excessive wear characteristics between the pawls and flywheel teeth exist with known starters.
It is an object of the invention to provide a pawl construction for internal combustion engine starters which limits eccentric misalignment of the starter and engine upon the occurrence of single pawl engagement, thus reducing stresses while protecting more vulnerable pulley sections with metal to metal contact points.
It is a further object of the invention to provide a pawl construction for internal combustion engine recoil starters wherein the configuration of the pawl causes the pawl to more rapidly extend relative to pulley rotation than previous designs and reduces the rotational pulley travel required to move both pawls out to the radius of the engagement teeth thus decreasing the possibility that only one pawl will engage.
Another object of the invention is to provide a pawl construction for recoil starters wherein the angle of engagement between the end of the pawl and the flywheel abutment teeth is improved to extend the life of the pawls and improve the mechanical characteristics of the engagement.
Yet another object of the invention is to provide a pawl construction for recoil starters wherein the pawls may be economically manufactured and are of a high strength design.
An additional object of the design is to provide a pawl construction for internal combustion engine starters which improves the engagement between a pawl and engine mounted abutment teeth upon the occurrence of eccentricity between the axis of rotation of the starter pulley and the engine starter structure and minimizes wear on the starter pulley.
It is another object of the invention to limit the maximum extension of the engaged pawl when the opposite pawl is not engaged and thus protect the pawl and its pivot socket from excessive stress.
In the practice of the invention a recoil starter for an internal combustion engine includes a pulley having a starter rope wound thereon. The pulley is rotatably mounted on a shaft and includes a hub, and a pair of pawls are pivotally mounted upon the hub. The pawls have an inner end of a cylindrical configuration so as to be pivotally received within cylindrical sockets defined in the pulley hub, and the outer ends of the pawls are capable of pivoting between radially extended and retracted positions. A pawl operator, in the form of a plate, is concentrically rotatably mounted upon the pulley shaft with a friction drag spring, and the operator plate includes configurations adapted to engage the pawls to radially outwardly extend the pawl outer ends, and also permit the pawl outer ends to radially retract inwardly during pulley recoiling.
The engine flywheel includes a plurality of abutment teeth defined on an annular ring or cup which are axially aligned with the pawls. As the pawls are extended outwardly the outer ends thereof will engage the abutment teeth and establish a positive driving connection between the starter pulley and engine flywheel to crank the engine for starting purposes. Retraction of the pawls releases the ends thereof from the abutment teeth to prevent interference and engagement when the engine begins to run or during pulley recoiling.
The pawls are provided with a knee or bend intermediate their inner and outer ends and this configuration defines an inwardly facing obtuse angle of the pawl regions adjacent the outer and inner ends. This configuration causes the pawl portion adjacent the pawl inner end to have an increased cam-angle with respect to the engagement with the pawl operating plate causing the pawl to outwardly extend quicker than with normal pawl constructions for a given degree of relative rotation between the pulley and plate. Additionally, the knee area is designed to contact the radially innermost portion of an abutment tooth when that pawl misses its engagement and significant eccentric deflection occurs. Further, the configuration of the pawl in accord with the invention causes the end region of the pawl adjacent the pawl outer end to approach a tangential relationship with respect to the movement of the engine flywheel abutment teeth thereby providing an improved angle of engagement between the pawl end and the abutment teeth with respect to wear and driving ability.
The pawls incorporating the inventive concepts may be formed of sheet metal by stamping operations, and in such instance a reinforcing gusset is preferably defined in the pawl knee, i.e. the transition bend between the pawl end regions.